California sea lion abundance estimation in Canada, 2020-21

Abstract

Abundance of California Sea Lions overwintering in southern British Columbia (BC) was estimated through five monthly aerial photographic surveys conducted from November 2020 to March 2021. The surveys were restricted to southern BC as few animals have been documented further north. California Sea Lion abundance was also estimated from the 2009-10 and 2017 Steller Sea Lion surveys which covered all sea lion haulouts in BC. To account for sea lions at sea and therefore not photographed during surveys, monthly correction factors derived from satellite tags deployed on sea lions in nearby Puget Sound (Washington, US) between 2014–16, were applied. The surveys flown in winter of 2009–10 and 2017 estimated 4,200 (95% CI 3,600–4,900) and 11,800 (95% CI 9,900–14,000) California Sea Lions, respectively. A mean abundance of 13,600 (95% CI 11,300–16,300) California Sea Lions was estimated in 2020–21. This represents a threefold increase since 2009–10 and no significant increase since 2017. While abundance remained consistent across monthly surveys in 2020–21, there was redistribution of animals. Potential Biological Removal (PBR) for 2020–21 in BC, using a recovery factor of 1.0 and adjusting for the proportion of time California Sea Lions spent in BC, was 433 individuals.